Destruction of the Lithosphere beneath the SW Margin of the São Francisco Craton Evidenced by Refertilized and Deformed Mantle Xenoliths

Abstract The destruction of the cratonic root has been documented for multiple cratons worldwide and is characterized by severe lithospheric thinning, extensive extensional deformation, and intense thermal activity. Here, we present detailed petrography accompanied by comprehensive geochemical and isotopic data for peridotites, pyroxenites, and eclogites from the SW margin of the São Francisco Craton that has also been severely thinned. The diamond-bearing Canastra-1 kimberlite represents a Cretaceous intrusion from the Alto Paranaíba Igneous Province and hosts garnet-bearing mantle xenoliths from different mantle sources, revealing a complex history of metasomatism/refertilization related to superimposed tectonic events since the cratonic consolidation. Eclogites (T = 978–982°C; P ~ 4.0 GPa) and pargasite-bearing websterites (T = 875–926°C; P = 2.0–3.0 GPa) represent the shallower and colder cratonic lithosphere. Mantle-derived high-MgO eclogitic clinopyroxenes show a light rare earth element (LREE)-enriched pattern (Ce/YbN = 60.90–93.63) while both clinopyroxene and garnet present high 87Sr/86Sr ratios (0.70842–0.70912) and negative εNd values (−5.6 to −7.3). These features, supported by the reconstructed whole-rock composition, suggest a mafic protolith probably metasomatized by fluid/melt derived from the overlying sedimentary rocks. Pargasite websterites are cumulates from an evolved (SiO2-rich) and hydrated basaltic andesitic magma. These xenoliths are characterized by high concentration of LREE relative to heavy-REE (HREE) in clinopyroxene (Ce/YbN = 10.52–50.61) and pargasite (Ce/YbN = 10.26–57.06), and by the presence of Al-rich orthopyroxene. As observed in eclogites, clinopyroxene and garnet from pargasite websterites display high 87Sr/86Sr ratios (0.70894–0.71094) and strong negative εNd values (−7.2 to −13.3). Trace elements (i.e. Zr, Ti, and Y) in garnets of both rock types indicate the role of a depleted component affected by a metasomatic agent. Although we were unable to date the formation of these rocks or the metasomatic events, we suggest a possible relationship with the consolidation of Gondwana during the Neoproterozoic. Sheared lherzolites, clinopyroxenites, anhydrous websterites, and dunite are deeper fragments from the lithosphere-asthenosphere boundary (LAB: 1191–1290°C; 5.3–5.6 GPa). They have abundant kelyphitic rims around garnet grains, which indicate metasomatism promoted by the percolation of a high-temperature proto-kimberli